The present invention relates to a system and method for identifying a faulty rotor position angle signal of a synchronous motor powered by a converter. The invention also relates to a computer with a computer program stored on a data carrier for carrying out the method and to a machine tool or production machine using the system and method.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Motors of electric drives are frequently powered and controlled by a converter. The motor control can include a field-based controller which decouples the field-producing and torque-producing current components. The current components can be decoupled, for example, by computing the current components in a coordinate system that rotates with the rotor flux of the motor. Such field-based controller requires information about the rotor position angle of the rotor for computing the flux angle in the motor. The rotor position angle can be measured by a transducer disposed on the motor and transmitted in form of a rotor position angle signal. However, when a transducer malfunctions with a field-based controller, the controller loses the information above the angle position of the rotating field in the motor. A reliable control of the motor with a field-based controller is then no longer possible.
The rotor position angle is frequently measured by the transducer incrementally without relying on an absolute reference position. The absolute position of the rotor in a stationary state is determined directly only at the time the motor is switched on. If an error occurs, the motor may continue to accelerate under certain unfavorable conditions (angle error between 90° and 270°) which can endanger the equipment or personnel. The same problem can occur if the incremental position indicator loses position markers.
To prevent endangering equipment or personnel, the drive must therefore be stopped as soon as possible, in particular when using linear motors with a limited range of travel, if a faulty rotor position angle signal is detected, or other measures must be taken.
It would therefore be desirable and advantageous to provide a system and method for identifying a faulty rotor position angle signal of a synchronous motor, to obviate prior art shortcomings and to allow safe operation of a synchronous motor powered by a converter if a faulty rotor position angle signal is detected.